The metallization of polymers has been the subject of several scientific studies Polymethylmethacrylate PMMA is known to have very bad adhesion to plasma deposited aluminum thin films. This study focuses on understanding the phenomena of adhesion between PMMA and metallic aluminum films deposited by magnetron sputtering. Before deposition, in situ pulsed DC plasma pre-treatment was performed in various atmospheres. We showed that oxygen-rich and short duration plasma pre-treatment considerably increase PMMA’s adhesives properties. Contact angle measurements showed a significant increase in the wettability of plasma pre-treated samples. XPS analysis revealed that the interaction between plasma species and polymer surface results in two simultaneous phenomena: surface functionalization by the introduction of oxygenated chemical functions such as carbonyl groups (Cdouble bondO) and surface degradation by the splitting of carbon chains by plasma UV radiation. Moreover, AFM analyses showed that the slight increase in surface roughness leads to best adhesion between PMMA and aluminum.